Behavioral, biochemical and pharmacological studies of active behavior in rats suggests that existence of basic arousal and suppresive systems which control their behavior in these situations. Furthermore, these data indicate that the cholinergic system is involved in mediating behavioral suppression. Detailed studies of the cholinergic system in two strains of rats which display opposite behavior in response to shock stress (one strain becomes active, the other strain becomes suppressed) will be undertaken to attempt to establish biochemical correlates in, and anatomical locations of the cholinergic systems which are involved in mediating this differential behavior. Experiments will also be undertaken to investigate the hypothesis that the cholinergically mediated suppressive system is in functional balance with a catecholaminergically mediated arousal system. Because of the complicated nature of the cholinergic system, its function will be evaluated by measuring a number of parameters, rather than on a single measure (Ach turnover by two independent methods, high affinity choline uptake, post synaptic receptor sensitivity). The studies will also involve microinjection of cholinergc agonists and antagonists into, and lesions of specific brain areas in conjunction with measurement of active avoidance behavior to further characterize the system. Though there is some danger in extrapolating behavior from animal models to man, the balance between arousal and suppression may also govern basic behavioral patterns in humans. Biochemical defects which occur in these regulatory systems might then contribute to various forms of maladaptive social behavior in response to environment stimuli. Therefore, a more complete understanding of the role of the cholinergic system in mediating suppressive behavior in animals will further our understanding of the biochemical basis for a basic behavioral system which may be of importance in human behavior.